When studying data analysis, we saw that a query was a technique of
isolating a series of columns and/or records of a table. Although this is usually done
for the purpose of data analysis, it can also be done to create a new list of
items for any particular reason. Most of the time, a query is created
temporarily, such as during data analysis while using a table, a form, or a web
page. After using such a temporary list, it is then dismissed. Many database
applications, including Microsoft SQL Server, allow you to create a query and be
able to save it for later use, or even to use it as if it were its own table.
This is the idea behind a view.

Definition

A view is a list of columns or a series of records retrieved
from one or more existing tables, or as a combination of one or more views and
one or more tables. Based on this, before creating a view, you must first decide
where its columns and records would come from. Obviously the easiest view is one whose
columns and records come from one table.

Practical Learning: Introducing Views

Start Microsoft Visual C# and create a new Windows Application named
YugoNationalBank1

In the Solution Explorer, right-click Form1.cs and click Rename

Type Central.cs and press Enter

Double-click the middle of the form and implement the Load event as
follows:

To create a data source, on the main menu, click Data -> Add New Data
Source...

In the first page of the wizard, make sure Database is selected and
click Next

In the combo box

If you see a YugoNationalBank2, select it

If you do not have YugoNationalBank2, click New
Connection... In the Server combo box, select the server or type
(local). In the Select Or Enter A Database Name combo box,
select YugoNationalBank2. Click Test Connection. Click OK twice. In the
Data Source Configuration Wizard, make sure the new connection is
selected and click Next. Change the Connection String to
csYugoNationalBank and click Next. Click the check box of Tables. Change the DataSet Name to dsYugoNationalBank

Click Finish

To create a new form, on the main menu, click Project -> Add Windows
Form...

Set the Name to AccountTypes and click Add

From the Data Sources window, drag the AccountTypes node and drop it on the form

To implement the electronic time, we will use two pieces of information
are required: an employee's number
and a starting period. After an employee has opened a time sheet:

The employee must first provide an employee number, which we will check in
the Employees table. If the employee
provides a valid employee number, we can continue with the time sheet. If
the employee number is invalid, we will let the user know and we cannot
continue with the time sheet

After the employee has provided a valid employee number, we will request
the starting period. After entering a (valid) date, we will check the time.
If there is a record that holds both the employee number and the start date,
this means that the employee had previously worked on a time sheet and we
will open that existing time sheet.

After the the employee or contractor has entered a valid
employee number and a start date, we will create a number called a time sheet
code, represented in the TimeSheet as the TimeSheetCode column. This number is
created as follows:

0000000000000

The first 5 digits represent the employee's number. The
second 4 digits represent the year of the start date. The next 2 digits
represent the month, and the last 2 digits represent the day. This number must
be unique so that there would not be a duplicate number throughout the time
sheet.

To make sure the value of the TimeSheetCode is unique for
each record, after the employee has provided a valid employee number and a start
date, we will create the time sheet code and check if that number exists in the
TimeSheet table already:

If that number exists already, this means that the employee has previously
worked on that time sheet and he or she simply wants to verify or update it.
We will then open the time values for that record and let the user view or
change it

If there is no record
with the specified time sheet code, we will conclude that the employee is working
on a new time sheet

In the Events section of the Properties window, double-click CloseUP and
implement the event as follows:

To create a view, you can use the Object Explorer (Microsoft
SQL Server Management Studio), a query window (Microsoft SQL Server Management
Studio), or the Server Explorer (Microsoft Visual Studio).
Before starting the view, you would have to specify the table(s) that would be involved.
To create a view from the Object Explorer or the Server Explorer,
you can expand the database, right-click Views and click
New View or Add New View. This would open the Add Table dialog box:

The basic functionality of this dialog box is
exactly the same as we reviewed for data analysis in the previous lesson:

To specify the table that would be used as the source, you
can click it in the list box of the Tables property page

If you will be using
another existing view, from the Views property page, you can click the name of
the desired view

If a function will be used to generate the records, you can
locate it in the Functions property page. After selecting the source object, you
can either double-click it or you can click it once and click Add. In the
previous lesson, we saw that you could add more than one existing table. In the same
way, you can add more than one view or functions

After
selecting the source(s), you can click Close on the Add Table dialog box

After
selecting the objects, as we saw in the previous lesson, they would display in the
window

As seen in the previous lesson, if you are using more than one table and
they are not (yet) related, you can drag a column from one table and drop it
on another table to create a JOIN between them

As we saw in previous lessons, to select a column, you can click its check box in the top
list. This would display it in the first empty box under the Column column and
would add its name to the SELECT statement. Alternatively, you can click
an empty box in the Column column to reveal its combo box, then click the arrow
of the combo box and select the desired column from the list

After selecting the column, its check box would be checked
in the top section of the window, its name would be displayed in the Column
column, and it would be added to the SELECT statement. If you know the
name of the column you want to add, you can manually type it in the SELECT
statement.

The structure of a view can be considered complete when the
SELECT statement is as complete as possible. At any time, to test the results of a view, you can run it.
To do this, in the Microsoft SQL Server Management Studio you can click the Execute SQL button
or in Microsoft Visual Studio, you can right-click the view and click Execute
SQL.
This would cause the bottom section of the view to display the results of the
query. Here is an example:

As reviewed during data analysis and when creating joins in
previous lessons, you can add conditions in a view to make it isolate only some
records. Here is an example:

The Name of a View

As stated already, one of the reasons for creating a view is to be able to use it over and over again. To
achieve this, the view must be saved. Like most objects in Microsoft SQL Server, a view
must have a name and it is saved as its own object. To save a view from the view window, you can click the Save button on the toolbar. You can also attempt
to close the window. You would then be prompted to save it. When saving a view,
you should give it a name that follows the rules and suggestions of SQL. In our lessons, here are the rules we will use to name our
views:

A name will start with a letter

After the first letter, the name will have combinations of underscores,
letters, and digits. Examples are n24, act_52_t

A name will not include special characters such as !, @, #, $, %, ^,
&, or *

A name will not have spaces

If the name is a combination of words, each word will start in uppercase

After saving a view, it becomes part of the Views node of
its database: a node would be created for it and its name would appear in the
Views node of its database.

Opening a View

As stated already, a view is a technique of selecting
records to view or use over an over again. After a view has been created,
you can open it. You have two main options.

To see the structure of a view, such as the table(s) on which it is
based and the relationships, if any that compose it, in the Object
Explorer, right-click the view and click Design

To see the SQL code that makes up a view, in the Object Explorer,
right-click the view and click Edit

Executing a View

Executing a view consists of seeing its results. To do this,
you have various options. To view the results of a view:

Open an empty query window associated with the database that contains the
view. In the query window, write a SELECT statement using the same
formulas and rules we saw for tables. Here is an example:

From the Object Explorer,
expand the database and its Views node. Right-click the name of the
view and click Open View

Practical Learning: Visually Creating a View

In the Server Explorer, expand the YugoNationalBank2 if necessary.
Right-click Views and click Add New View

In the Add Table dialog box, click Employees, click Add, and
click Close

In the Diagram section of the view, click the check boxes of EmployeeID
and EmployeeNumber

Open the Account's Transactions form, enter an account number and click
Locate

Close the forms and return to your programming environment

Programmatically Creating and Using a View

Creating a View

To programmatically create a view, you use the following SQL
syntax:

CREATE VIEW ViewName
AS
SELECT Statement

If you are using Microsoft SQL Server Management Studio, it can generate skeleton code of a view
for you. To use it, first create an empty query window. Display the Template
Explorer. In the Template Explorer, expand the View node. From the View node,
drag Create View and drop it in the query window.

The creation of a view starts with the CREATE VIEW
expression followed by a name. The name of a view follows the rules
and suggestions we reviewed for view names. After the name of the view, use the AS
keyword to indicate that you are ready to define the view.

Because a view is primarily a SQL statement, it is defined using a SELECT
statement, using the same rules we studied for data analysis. Here is an example
of a view:

After creating the SQL statement that defines the view, you
must execute the statement. If using a query window in Microsoft SQL Server
Management Studio, you can do this by pressing
F5. Once the statement is executed, its name is automatically added to the Views
node of its database even if you do not save its code.

After creating a view, it shares many of the characteristics
of a table. For example, a view has its own columns although the columns are
actually tied to the table(s) that hold(s) the original data. Treated as a
table, you can access the columns of a view using a SELECT
statement. This means that you can access one, a few, or all of the columns.
Here is an example that accesses all columns of a view:

SELECT PayrollPreparation.* FROM PayrollPreparation;

View Maintenance

The Properties of a View

In Transact-SQL, a view is considered an object. As
such, it can be viewed, changed, or deleted. Like any regular object, a
view has its own characteristics. To see them in Microsoft SQL Server
Management Studio, you can right-click the
view and click Properties. A View Properties dialog box would come up. It
can give you information such as the name of the database the view belongs
to, the date the view was created, etc.

Modifying a View

After a view has been created, either by you or
someone else, you may find out that it has an unnecessary column, it needs
a missing column, it includes unnecessary records, or some records are
missing. Fortunately, you can change the structure or the code of a view. This is
referred to as altering a view. You have various options:

To visually change a view, in the Object Explorer of Microsoft SQL Server
Management Studio, you can right-click the view
and click Design. In the Server Explorer of Microsoft Visual Studio, you can
right-click the view and click Open View Definition.
From the view window, you can add or remove the columns.
You can also change any options in one of the sections of the window. After
modifying the view, save it and close it

To change the code of a view, in the Object Explorer of Microsoft SQL Server
Management Studio, right-click it and
click Edit. After editing the
view's code, you can save it

From the Object Explorer of Microsoft SQL Server Management Studio, you can right-click the view, position the mouse on
Script View As -> ALTER To -> New Query Editor Window

The basic formula to programmatically modify a view
is:

ALTER VIEW ViewName
AS
SELECT Statement

You start the alteration with the ALTER VIEW
expression followed by the name of the view. After the name of the view,
use the AS keyword to specify that you are ready to show the
change. After the AS keyword, you can then define the view as you see fit.
For example, you can create a SELECT statement that includes a
modification of the existing code or a completely new statement.

In the view we created to show a list of men of a table, we
included a column for the sex. This column is useless or redundant because we
already know that the list includes only men. Here is an example of altering the
view to remove (or rather omit) the Sex column of the Persons table:

Instead of modifying a view, if you find it altogether
useless, you can remove it from its database. You have various options. To delete a view:

In the Object Explorer in Microsoft SQL Server Management Studio,
right-click the name of the view and click Delete. The Delete Object dialog
box would display to give you the opportunity to confirm your intention or
to change your mind

In the Object Explorer in Microsoft SQL Server Management Studio, right-click the view, position the mouse on Script
View As -> DROP To New Query Editor Window

In Microsoft SQL Server Management Studio, you can open an empty query window associated with the database that has the
undesired view. From the Template Explorer, in the View node, drag Drop View
and drop it in the query window

In the Server Explorer in Microsoft Visual Studio, under the Views node
of the database, you can right-click the view and click Delete. A message
box would display, asking you whether you are sure you want to delete the
view. You can decide to continue or change your mind

The formula to programmatically delete a view is:

DROP VIEW ViewName

On the right side of the DROP VIEW expression, enter
the name of the undesired view and execute the statement. You will not be
warned before the interpreter deletes the view. If you are
programmatically creating a Windows application, of course you can use a
conditional statement to assist the user with deciding whether to
continue deleting the view or not.

Using a View

Data Entry With a View

As seen so far, a view is a selected list of records from a
table. As you may suspect, the easiest view is probably one created from one
table. Imagine you have a table of employees and you want to create a view that
lists only their names. You may create a view as follows:

On such a view that is based on one table, you can perform
data entry, using the view, rather than the table. To do this, you follow the
same rules we reviewed for table data entry. Here is an example:

If you perform data entry using a view, the data you provide
would be entered on the table from which the view is based. This means that the table would be updated
automatically. Based on this feature, you can create a view purposely intended
to update a table so that, in the view, you would include only the columns that
need to be updated.

To create more complex or advanced views, you can
involve functions. As always, probably the easiest functions to use are
those built-in. If there is no built-in function that performs the
operation you want, you can create your own. Here is an example:

It is important to know that a view is more of a table
type than any other object. This means that a view is not a function but
it can use a function. The word argument here only means that some values
can be passed to a view but these values can be specified only when
creating the view. They are not real arguments.

When structuring a view, you can create placeholders for
columns and pass them in the parentheses of the view. This would be done
as follows:

If you use this technique, the names passed in the
parentheses of the view are the captions that would be displayed in place
of the columns of the view. This technique allows you to specify the
strings of your choice for the columns. If you want a column header to
display the actual name of the column, write it the same. Otherwise, you
can use any string you want for the column. If the name is in one word,
you can just type it. If the name includes various words, include them
between an opening square bracket "[" and a closing square
bracket "]".

After listing the necessary strings as the captions of
columns, in your SELECT statement of the view, you must use the
exact same number of columns as the number of arguments of the view. In
fact, each column of your SELECT statement should correspond to an
argument of the same order.

Because, as we stated already, a view is not a
function and the values passed to the view are not real arguments, when
executing the view, do not specify the names of arguments. Simply create a
SELECT statement and specify the name of the view as the source.

Views and Conditional Statements

Besides its querying characteristics that allow it to
perform data analysis, probably the most important feature of a query is
its ability to be as complex as possible by handling conditional
statements. This makes it possible to use a view instead of a table in
operations and expressions that would complicate the code or structure of
a table. When creating a view, in its SELECT statement, you can
perform column selections, order them, and set criteria to exclude some
records.